Edible plastified products comprising a continuous fat phase and a dispersed gas phase are well known. Incorporation of e.g. air in margarine or shortening may have a beneficial effect on the properties of such products.
A. J. C. Andersen and P. N. Williams describe in Margarine, 2nd revised edition, Pergamon Press (1965), pp. 313-314, packets of margarine having a large volume in relation to their weight because of the even distribution of 15-40% finely divided gas throughout the margarine. The gas is air or inert gas such as nitrogen. Such gas-containing margarine is said to spread more easily at low temperatures, to give easier mixing in domestic cake-making, to spatter less when used in frying, to have better shortening properties and greater resistance to mould growth. For the manufacture of such margarine, reference is made to U.S. Pat. Nos. 2,937,093 and 2,970,917.
U.S. Pat. No. 2,937,093 describes the manufacturing of whipped fatty product emulsions such as margarine containing more than 20 vol. % of gas. The process comprises whipping a fatty composition to incorporate gas therein, chilling the whipped emulsion with violent agitation, holding it to permit setting of the product emulsion while transporting it, substantially terminating working of the product emulsion upon setting and cutting the set product emulsion. The preferred gas used in the process is nitrogen. The specification aims at providing a process to prepare products such as whipped margarine which are divided into unit portions and packaged via solid filling, using traditional packaging equipment instead of having to introduce the whipped product into open cups or containers in a flowable condition, the so-called liquid filling.
According to U.S. Pat. No. 2,970,917 the "mouthing" qualities, rate of flavour release, stability, resistance to mould growth, spreadability in the cold, break coverage, resistance to "oiling off" at room temperature, frying properties and baking performance of margarine can be improved by incorporating therein, in a specified way, about 15-40 vol. % of finely and uniformly dispersed inert gas, e.g. air, carbon dioxide, nitrogen etc. The product is prepared by incorporating the gas in a liquid margarine emulsion. The composition is then plastified by cooling and agitating it at super-atmospheric pressure, e.g. in a Votator, to produce a flowable mass and then the pressure on the flowable mass is released to atmospheric level, prior to packaging. The flowable mass can be filled into a moulding zone after the pressure has been released to allow expansion of the gas. It is said that, should the flowable mass be confined within the mould under positive pressure during the time of setting up, subsequent gas expansion varies from surface to the centre of the moulded product, with the result that fracturing of the product occurs and variation in porosity and colour are noted.
As an alternative to the above described liquid filling, the specification describes how the product can be packaged via solid filling. In that case, the still workable mass is passed through an orifice having the desired cross-section of a print at low temperature, chilling the extruded solid product to obtain case hardening, cutting the extruded product to proper length, wrapping and cartoning it.
In practice, the above described processes often do not give satisfactory results. It can, for example, be undesirable to employ liquid filling. With liquid filling the network of fat crystals, which largely determines the ultimate structural properties of the product, is formed to a considerable extent after the packaging, during storage. In particular for relatively hard products this may be unsuitable. It may, for example, cause such products to be brittle. In such cases, to impart the desired structural properties to the product, it is often necessary to cause the network of crystals to form to a large extent during the process prior to packaging and to employ solid filling to divide the product into unit portions.
With solid filling, similar problems occur as described above for liquid filling if the flowable mass is confined within the mould under super-atmospheric pressure while it is setting. In the solid filled product, the gas distribution often is inhomogeneous, the amount of dispersed gas and the average bubble size being larger near the surface than in the centre of the product, causing, inter alia, colour variation to occur. In some cases, a foam layer may form on the surface.
Whether applying solid or liquid filling, in practice often problems arise to control the amount of dispersed gas in the end product. The beneficial effects of the gas are generally ascribed to the dispersed gas and dissolved gas supposedly does not contribute. The amount of dispersed gas in the end product is often subject to substantial variations even though the amount of gas included in the composition during the preparation is kept constant. This not only affects the quality of the product per se, but also leads to variation in the weight/volume ratio of the product which is undesirable, whether the division of the product in unit portions is done on a weight basis or on a volume basis.